Update concepts-architecture-overview.md (#6855)
Update concepts-architecture-overview.md (#6855)

Added zookeeper role
merlimat/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,yahoo/pulsar